Characterization of parasitics in TO-packaged high-speed laser modules

An elaborate analysis of the parasitic network of high-speed through-hole packaging (TO)-type laser modules is presented using a small-signal equivalent circuit model. The intrinsic laser diode is obtained using the optical modulation technique, and is embedded into the model as a separate component. Three step-by-step measurements are made for determining the packaging parasitic network, including the test fixture, TO header, submount, bonding wire, and parasitics of the laser chip. A good agreement between simulated and measured results confirms the validation and accuracy of the characterization procedures. Furthermore, several key parasitic elements are found based on the simulation of the high-frequency responses of the packaged devices. It is expected that the 3-dB bandwidth of 12 GHz or more of the low-cost TO packaged laser module may be achieved using the proposed optimization method.

Structural characterization of AlGaN/GaN superlattices by x-ray diffraction and Rutherford backscattering

We report on structural characterization of AlGaN/GaN superlattices grown on sapphire. The superlattice formation is evidenced by high-resolution x-ray diffraction and transmission electron microscopy. The high resolution x-ray diffraction spectra exhibit a pattern of satellite peaks. The in-plane lattice constants of the superlattices indicate the coherent growth of the AlGaN layer onto GaN. The average At composition in the superlattices is determined to be 0.08 by Rutherford backscattering spectroscopy. The average parallel and perpendicular elastic strains for the SLs are determined to be (e(parallel to)) = +0.25% and (e(perpendicular to)) = -0.17%. (c) 2006 Elsevier Ltd. All rights reserved.

Preparation and characterization of the stable nc-Si/a-Si : H films

High-quality nc-Si/a-Si:H diphasic films with improved stability were prepared by using the plasma-enhanced chemical vapor deposition technology. In comparison with typical amorphous silicon, the diphasic silicon films possess higher photoconductivity (two orders larger than that of the amorphous silicon film) and fairly good photosensitivity(the ratio of the photo-to dark-conductivity is about 10) and higher stability (the degradation of the photoconductivity is less than 10% after 24h long light soaking with 50 mW/cm(2) intensity at room temperature). In addition, the diphasic silicon film has a better light spectra response in the longer wavelength range. The improvement in photoelectronic properties may be attributed to: the existence of the disorder within the amorphous matrix, which breaks the momentum selection rule in the optical transition and, consequently, results in the large light absorption coefficient and high photosensitivity; the improved medium range order and low gap states density. Excess carriers generated in the amorphous matrix tend to recombine in the embedded crystallites, which suppresses nonradiative recombination within the amorphous matrix and reduces the subsequent defect creation.

Structure and optical properties of upper In(Ga)As quantum dots on a different seed layer with a thin GaAs spacer layer

The structure and optical properties of In(Ga)As grown with the introduction of InGaAlAs or InAlAs seed dots layers are investigated. The area density and size homogeneity of the upper InGaAs dots are efficiently improved with the introduction of a layer of high-density buried dots. When the GaAs spacer layer is too thin to cover the seed dots, the upper dots exhibit the characterization of a quantum well. By analyzing the growth dynamics, we refer to it as an empty-core structure dot. (C) 2002 Elsevier Science B.V. All rights reserved.

Fabrication and characterization of metal-semiconductor-metal (MSM) ultraviolet photodetectors on undoped GaN/sapphire grown by MBE

Interdigital metal-semiconductor-metal (MSM) ultraviolet photoconductive detectors have been fabricated on undoped GaN films grown by molecular beam epitaxy (MBE), Response dependence on wavelength, applied current, excitation powers and chopper frequency has been extensively investigated. It is shown that the photodetector's spectral response remained nearly constant for wavelengths above the band gap and dropped sharply by almost three orders of magnitude for wavelengths longer than the band gap. It increases linearly with the applied constant current, but very nonlinearly with illuminating power. The photodetectors showed high photoconductor gains resulting from trapping of minority carriers (holes) at acceptor impurities or defects. The results demonstrated the high quality of the GaN crystal used to fabricate these devices. (C) 2000 Elsevier Science B.V. All rights reserved.

Characterization of CdSe and CdSe/CdS core/shell nanoclusters synthesized in aqueous solution

CdSe nanoclusters overcoated with CdS shell were prepared with macapoacetic acid as stabilizer. The optical properties of CdSe nanoclusters and the influence of CdS shell on the electronic structures of CdSe cores were studied by optical absorption, photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies. Based on PL and PLE results and the theoretical calculation on fine structure of bandedge exciton, a model of formation of excimer within the small clusters was proposed to explain the large Stokes shift of luminescence from absorption edge observed in PL results. (C) 2000 Elsevier Science B.V. All rights reserved.

X-ray double-crystal characterization of the strain relaxation in GaAs/GaNxAs1-x/GaAs(001) sandwiched structures

An X-ray diffraction method, estimating the strain relaxation in an ultrathin layer, has been discussed by using kinematic and dynamical X-ray diffraction (XRD) theory. The characteristic parameter Delta Omega, used as the criterion of the strain relaxation in ultrathin layers, is deduced theoretically. It reveals that Delta Omega should be independent of the layer thickness in a coherently strained layer. By this method, we characterized our ultrathin GaNxAs1-x samples with N contents up to 5%. XRD measurements show that our GaNxAs1-x layers are coherently strained on GaAs even for such a large amount of N. Furthermore, a series of GaNxAs1-x samples with same N contents but different layer thicknesses were also characterized. It was found that the critical thickness (L-c) of GaNAs in the GaAs/GaNAs/GaAs structures determined by XRD measurement was 10 times smaller than the theoretical predictions based on the Matthews and Blakeslee model. This result was also confirmed by in situ observation of reflection high-energy electron diffraction (RHEED) and photoluminescence (PL) measurements. RHEED observation showed that the growth mode of GaNAs layer changed from 2D- to 3D-mode as the layer thickness exceeded L-c. PL measurements showed that the optical properties of GaNAs layers deteriorated rapidly as the layer thickness exceeded L-c. (C) 2000 Elsevier Science B.V. All rights reserved.

Optical properties of InAs self-organized quantum dots in n-i-p-i GaAs superlattices

The optical properties of InAs quantum dots in n-i-p-i GaAs superlattices are investigated by photoluminescence (PL) characterization. We have observed an anomalously large blueshift of the PL peak and increase of the PL linewidth with increasing excitation intensity, much smaller PL intensity decrease, and faster PL peak redshift with increasing temperature as compared to conventional InAs quantum dots embedded in intrinsic GaAs barriers. The observed phenomena can all be attributed to the filling effects of the spatially separated photogenerated carriers. (C) 2000 American Institute of Physics. [S0003-6951(00)03515-4].

Growth and characterization of GaN on LiGaO2

The nearly lattice-matched (0 0 1)LiGaO2 substrates have been used for the growth of GaN by LP-MOVPE, GaN epilayers have been grown on both domains at very low input partial pressure of hydrogen and relatively low growth temperature. The differences in the growth rate, crystal and optical qualities of hexagonal GaN epilayers grown on LiGaO2 substrate with two polar domains are investigated. LiGaO2 single crystal with a single domain structure and an adequate surface plane is a promising substrate for the growth of high quality of hexagonal GaN thin films. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

Growth and characterization of InGaAs/InAlAs/InP high-electron-mobility transistor structures towards high channel conductivity

High-quality InGaAs/InAlAs/InP high-electron-mobility transistor (HEMT) structures with lattice-matched or pseudomorphic channels have been grown by molecular-beam epitaxy (MBE). The purpose of this work is to enhance the channel conductivity by changing the epitaxial structure and growth process. With the use of pseudomorphic step quantum-well channel, the highest channel conductivity is achieved at x = 0.7, the corresponding electron mobilities are as high as 12300 (300 K) and 61000 cm(2)/V.s (77 K) with two-dimensional electron gas (2DEG) density of 3.3 x 10(12) cm(-2). These structures are comprehensively characterized by Hall measurements, photoluminescence, double crystal X-ray diffraction and transmission electron microscopy. Strong room-temperature luminescence is observed, demonstrating the high optical quality of the samples. We also show that decreasing the In composition in the InyAl1-yAs spacer is very effective to increase the 2DEG density of PHEMT structures. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

Characterization of bulk ZnO single crystal grown by a CVT method - art. no. 68410F

Hall effect, photoluminescence spectroscopy (PL), mass spectroscopy and X-ray diffraction have been used to study bulk ZnO single crystal grown by a closed seeded chemical vapor transport method. Enhancement of n-type electrical conduction and increase of nitrogen concentration are observed of the ZnO samples after high temperature annealing. The results suggest that vacancy is dominant native defect in the ZnO material. These phenomena are explained by a generation of shallow donor defect and suppression of deep level defects in ZnO after the annealing.

Characterization of AlGaN on GaN template grown by MOCVD - art. no. 68410K

AlxGa1-xN layer was grown on sapphire substrate with GaN template by Metal Organic Chemical Vapor Deposition system (MOCVD). High temperature A1N (HT-A1N) interlayer was inserted between AlxGa1-xN layer and GaN template to solve the cracking problem that often appears on AlxGa1-xN surface when directly grown on high temperature GaN template. Optical microscope, scanning electron microscopy (SEM), atomic force microscope (AFM), high resolution x-ray diffraction (HRXRD) and cathodoluminescence (CL) were used for characterization. It was found that the cracking was successfully eliminated. Furthermore, the crystalline quality of AlxGa1-xN layer with HT-A1N interlayer was much improved. Interference fringes were found in the HRXRD images. CL test showed that yellow emission was much reduced for AlGaN layer with HT-A1N interlayer.

Fabrication and characterization of TO packaged high-speed laser modules - art. no. 682407

Various high-speed laser modules are fabricated by TO-Packaged processes, such as FP laser modules, DFB laser modules, and VCSEL modules. Furthermore,, the resonance among the circuit elements provides an approach to compensating the TO packaging parasitics, and improving the frequency response of the devices. The detailed equivalent circuit model is established to investigate both the laser diode and packaging comprehensively. The small-signal modulation bandwidths of the TO packaged FP laser, DFB laser and the VCSEL modules are more than 10, 9.7 and 8 GHz, respectively.

Homoepitaxial growth and characterization of 4H-SiC epilayers by low-pressure hot-wall chemical vapor deposition

Horizontal air-cooled low-pressure hot-wall CVD (LP-HWCVD) system is developed to get high quality 4H-SiC epilayers. Homoepitaxial growth of 4H-SiC on off-oriented Si-face (0001) 4H-SiC substrates purchased from Cree is performed at a typical temperature of 1500 degrees C with a pressure of 40 Torr by using SiH4+C2H4+H-2 gas system. The surface morphologies and structural and optical properties of 4H-SiC epilayers are characterized with Nomarski optical microscope, atomic force microscopy (AFM), x-ray diffraction, Raman scattering, and low temperature photoluminescence (LTPL). The background doping of 32 pm-thick sample has been reduced to 2-5 x 10(15) cm(-3). The FWHM of the rocking curve is 9-16 arcsec. Intentional N-doped and B-doped 4H-SiC epilayers are obtained by in-situ doping of NH3 and B2H6, respectively. Schottky barrier diodes with reverse blocking voltage of over 1000 V are achieved preliminarily.

Tellurium enhanced non-resonant third-order optical nonlinearity in a germano-silicate optical fiber

碲掺杂的高非线性石英光纤